Oncodevelopmental Biology and Medicine, 4 (1983) 219-229 ARE THERE FACTORS PREVENTING CANCER DEVELOPMENT DURING EMBRYONIC LIFE? Department of Oncology of the Karolinska Institute and Hospital (Radiumhemmet) and the NationalBacteriological Laboratory, S-104 01 Stockholm, Sweden On the basis of the following literature observations, a hypothesis is advanced that the development ofcancer is a